1. Field of the Invention
The present invention relates to a head positioning mechanism for a magnetic disc device. In particular, the present invention relates to a head positioning mechanism for a magnetic disc device having a fine tracking actuator.
2. Description of the Related Art
A conventional magnetic disc device, as shown in FIG. 13, makes a magnetic head 54 move by a carriage 52 and a support spring 53, which are integrally coupled to a single main actuator 51. However, with a higher track density, an improvement in accuracy of positioning the head has been increasingly demanded. As a means for satisfying the demand, there has been proposed a technique using a fine tracking actuator for moving the respective magnetic heads by a very short distance in addition to the main actuator.
For example, Japanese Patent Unexamined Publication No. Hei 2-263369 and Japanese Patent Unexamined Publication No. Hei 4-232678 disclose a device using a fine displacement generating element as a fine tracking actuator. In this conventional example, in the case of conducting a head coarse seek operation that allows the main actuator to be moved, the rigidity of the element per se prevents the support spring from greatly fluctuating, resulting in an advantage that control is facilitated. In this conventional example, during the head coarse seek operation, the operation of the fine displacement generating element is stopped, and the main actuator is driven. On the other hand, after the completion of the head coarse seek operation, the main actuator is stopped, and a head fine seek operation is conducted. In other words, the fine displacement generating element is driven on the basis of a position error signal from the magnetic head to realize a fine head positioning operation.
Also, in a lecture report of Japan Machinery Association, IIP'96 (Information, Intelligence, and Precision Machine Section), "A high-compliance type fine tracking actuator of a magnetic disc device," a fine tracking actuator employing an electromagnetic force shown in FIG. 14 has been announced.
However, in the former conventional example using the fine displacement generating element, since a high voltage is required to drive the fine displacement generating element, and a long-period reliability of the element per se is low, etc., there is such a disadvantage that the utility is low. Also, in the latter conventional example using the electromagnetic force, because the fine tracking actuator is not perfectly fixed to a carriage during the head coarse seek operation that makes the main actuator move, a relative positional relationship between the carriage and the support spring is not determined by only one variable at the time of starting the head fine seek operation that makes the fine tracking actuator and the main actuator operate simultaneously. This results in a disadvantage that the control of the fine tracking actuator becomes difficult.